[Amps] SB-200 Problem

[Peter Chadwick]

Rich said;

>EUR  no RF input is needed when it makes its own.

I would be inclined to do the first sets of tests with a 50 ohm load on the
output, and the transceiver connected to the input (transceiver in transmit, but
delivering NO power). That way, the amp is seeing something like reality as far
as source and load impedances are concerned. When it's stable that way, you can
try the 'no input - no output load' - it ought to be stable like that.  572Bs
aren't the easiest of bottles to tame as far as parasitics go - the internal
structure has a lot of inductance, and if new ones have a bit higher gain, it
could easily tip the balance. I suspect that the amount of suppression
inductance needed ends up being such that of necessity, a fair amount of power
will get dumped in the suppression resistors. This means that 10metre efficiency
will be down, although the suppressors will help keep the room warm.......

I believe that 572Bs were originally intended as Class B zero bias (or nearly
so) AF power tubes for AM modulators.

73

Peter G3RZP